On-chip communications between memory channels and a central processing unit (CPU) may be serviced by a bus having a single port to access address space provided by the memory channels. Transactions, such as read and/or write requests, may target different types of memory, such as cacheable, non-cacheable, device, and strongly-ordered memory types. Protocols governing the function of the bus may specify that transactions having the same identifier and/or targeting the same type of memory are transmitted to a requested memory channel in order, and responses are returned in order. Order can be maintained by keeping track of identifiers for every outstanding transaction on all outgoing ports, enabling transaction requests and/or responses to be reordered based on the tracked information. However, such tracking involves memory resources and associated logic to store and process the tracked information, and can result in processing delays.
A transaction identifier may represent a memory type, such as cacheable, non-cacheable, device, and strongly-ordered memory types. Typically, transactions of a particular memory type are targeted to a particular memory channel; however it is possible for transactions having the same memory type to target different memory channels. As indicated above, it may be desirable to maintain transaction ordering per identifier. For example, in certain settings, it can be important to perform order tracking for all transactions targeting strongly ordered memory in order.